Tcl_DetachPids may be called to ask Tcl to take responsibility for one or more processes whose process ids are contained in the pidPtr array passed as argument. The caller presumably has started these processes running in background and doesn't want to have to deal with them again.
Tcl_ReapDetachedProcs invokes the waitpid kernel call on each of the background processes so that its state can be cleaned up if it has exited. If the process hasn't exited yet, Tcl_ReapDetachedProcs doesn't wait for it to exit; it will check again the next time it is invoked. Tcl automatically calls Tcl_ReapDetachedProcs each time the exec command is executed, so in most cases it isn't necessary for any code outside of Tcl to invoke Tcl_ReapDetachedProcs. However, if you call Tcl_DetachPids in situations where the exec command may never get executed, you may wish to call Tcl_ReapDetachedProcs from time to time so that background processes can be cleaned up.
Tcl_WaitPid is a thin wrapper around the facilities provided by the operating system to wait on the end of a spawned process and to check a whether spawned process is still running. It is used by Tcl_ReapDetachedProcs and the channel system to portably access the operating system.
Copyright © 1989-1993 The Regents of the University of California. Copyright © 1994-1996 Sun Microsystems, Inc. Copyright © 1995-1997 Roger E. Critchlow Jr.